How to make calls in Nha Trang without buying a local SIM card?

Video calls don't use much data, and Wi-Fi is good almost everywhere — hotels have great connections, and as a backup you can use the Wi-Fi at McDonald's, which is even good enough to work remotely from.

If you don't have a local SIM, the simplest option is to turn on roaming with your home carrier and add a calling package — it works, though it's not the cheapest option.

Actually, you don't even need to activate roaming — calls often go through on your regular plan without turning on any roaming settings at all.